Effect And Mechanism Of Selenoprotein P On ICAM1 In Autoimmune Thyroiditis

Objective: Autoimmune Thyroiditis(AIT)is one of the common endocrine system diseases.Its main features are the presence of infiltrating lymphocytes in the thyroid gland and the presence of thyroglobulin antibody(TGAb)and thyroid peroxidase antibody(TPOAb)in the serum.Its symptoms are mainly inflammatory destruction.Infiltrating lymphocytes are mainly T cells and B cells,of which T cells produce and release cytokines under the stimulation of thyroid autoantigens,such as interferon-?(IFN-?),interleukin-1?(IL1-?),and tumor necrosis factor-?(TNF-?)and so on.Under the stimulation of these cytokines,inflammatory cytokines that were not originally expressed in thyroid cells appear to be highly expressed,such as intercellular adhesion molecule 1(ICAM1).These inflammatory factors can further promote the development of inflammation.Studies have shown that the overexpression of ICAM1 in thyroid cells from patients with AIT is due to abnormal epigenetic modifications.In the thyroid cells,the ICAM1 promoter region,which should be modified by hypermethylation,changes the methylation state that should normally be maintained,resulting in abnormally high gene expression.It is not clear whether cytokines such as IFN-? stimulate the high expression of ICAM1 by reducing the methylation status.Selenium is an essential trace element in the human body.It plays important physiological and biochemical functions in the body,such as antioxidant and anti-aging effects.Selenium exerts its biological function in the body mainly in the form of selenoprotein.Its importance to the reproductive system,immune system,and thyroid function has been established and is extremely important to human health.Selenoproteins such as SEPP1 can protect thyroid cells from oxidative damage and regulate thyroid hormone synthesis,activation,and metabolic processes.Studies have reported that selenium status and selenium supplementation have an effect on global and gene-specific methylation.However,whether the selenoprotein SEPP1 can down-regulate the expression of ICAM1 by changing the methylation level of the promoter region,thereby protecting thyroid cells from inflammatory damage,remains to be confirmed.This study uses a combination of in vivo and in vitro experiments to explore the anti-autoimmune thyroiditis effect of selenoprotein SEPP1 and its possible mechanism.The research results can further elaborate the pathogenesis of autoimmune thyroiditis and provide a theoretical basis for exploring effective prevention and treatment programs for the disease.Methods: 1.Population-based study:This study included 40 female subjects,The subjects' thyroid function indexes FT3,FT4 and TSH are within the normal range,including 20 cases with high TPOAb or TGAb and HE staining of thyroid tissue with lymphocyte infiltration included in the autoimmune thyroiditis group(AIT group),20 cases of TPOAb or TGAb were in the normal range and HE staining was not seen Lymphocyte-infiltrated thyroid tissue was included in the control group(Control group).Thyroid tissue was obtained during surgery,Isolate thyroid cells.qRT-PCR and immunohistochemical methods to detect mRNA and protein expression levels of ICAM1,one-generation sequencing method to detect methylation levels of ICAM1 promoter region,qRT-PCR and immunohistochemical methods to detect mRNA and protein expression levels of selenoprotein SEPP1.2.Vitro study: nthy-ori 3-1 cell line(human thyroid cell line)was treated with serum-free medium containing 1000U/ml interferon-? for 24 h,and a serum-free control group was set up.The mRNA expression levels of ICAM1,the methylation level of ICAM1 promoter region and the mRNA expression level of selenoprotein SEPP1 were measured in the same way as above.Interferon-? induced ICAM1 overexpression cell model was treated with 0 ?M,0.5 ?M,1.5 ?M,5 ?M sodium selenite for 24 h,48h,72 h,96h to detect the expression level of ICAM1 mRNA.The methylation level of ICAM1 promoter region was detected in the same way.3.The results were statistically analyzed with SPSS 20.0.The difference was statistically significant at P <0.05.Result: 1.Population study: 1.1 The age and gender of the subjects in the AIT group were not statistically different from those in the Control group.The serum TSH and FT4 in the AIT group were not statistically different from those in the Control group.Although the FT3 in serum was statistically different,the FT3 in the selected population was within the normal range.The serum TPOAb and TGAb of the AIT group were higher than those of the Control group,and the difference was statistically significant(P <0.05).1.2 The m RNA and protein expression level of ICAM1 in thyroid cells of the AIT group was higher than that of the Control group,and the difference was statistically significant(P <0.05).1.3 The methylation rate of-163 bp,-64 bp,-20 bp,-18 bp upstream of ICAM1 transcription start site(TSS)in thyroid cells in AIT group was lower than that in Control group(P <0.05).1.4 The mRNA and protein expression level of SEPP1 in thyroid cells in the AIT group was lower than that in the Control group,the difference was statistically significant(P <0.05).2.In vitro studies: 2.1 The expression level of SEPP1 mRNA in IFN-? treatment group was lower than that in Control group,the difference was statistically significant(P<0.05).The mRNA expression level of ICAM1 was higher than the control group,the difference was statistically significant(P <0.01).The methylation levels of-179 bp,-163 bp,-125 bp,and-102 bp upstream of the start site(TSS)were significantly lower than those in the Control group(P <0.05).2.2 After sodium selenite treatment of thyroid cell lines for 72 h and 96 h,the mRNA expression level of ICAM1 decreased in a concentration-dependent manner;the methylation rates of-163 bp and-125 bp increased in a concentration-dependent manner.Conclusion: SEPP1 may reduce the expression of ICAM1 in the thyroid by increasing the methylation level of the ICAM1 promoter region,thereby protecting the thyroid from damage.